Download 26-2 The Kidneys

Chapter 26
The Urinary System
Lecture Presentation by
Lee Ann Frederick
University of Texas at Arlington
© 2015 Pearson Education, Inc.
Figure 26-1 An Introduction to the Urinary System.
Organs of the
Urinary System
Kidney
Produces urine
Ureter
Transports urine
toward the
urinary bladder
Urinary bladder
Temporarily stores
urine prior
to urination
Urethra
Conducts urine to
exterior; in males,
it also transports
semen
© 2015 Pearson Education, Inc.
Anterior view
26-1 Urinary System Functions
• Three Functions of the Urinary System
1. Excretion
• Removal of organic wastes from body fluids
2. Elimination
• Discharge of waste products from body
3. Homeostatic regulation
• Of blood plasma volume and solute concentration
© 2015 Pearson Education, Inc.
26-1 Urinary System Functions
• Functions of the Urinary System
• Kidneys — organs that produce urine
• Urinary tract — organs that eliminate urine
• Ureters (paired tubes)
• Urinary bladder (muscular sac)
• Urethra (exit tube)
• Urination or micturition — process of eliminating
urine
• Contraction of muscular urinary bladder forces
urine through urethra, and out of body
© 2015 Pearson Education, Inc.
26-1 Urinary System Functions
• Homeostatic Functions of the Urinary System
• Regulates blood volume and blood pressure
• By adjusting volume of water lost in urine
• Releasing erythropoietin and renin (O2 levels)
• Regulates plasma ion concentrations
• Sodium, potassium, and chloride ions (by
controlling quantities lost in urine)
• Calcium ion levels (through synthesis of calcitriol)
© 2015 Pearson Education, Inc.
26-1 Urinary System Functions
• Homeostatic Functions of Urinary System
• Helps stabilize blood pH
• By controlling loss of hydrogen ions and
bicarbonate ions in urine
• Conserves valuable nutrients
• By preventing excretion while excreting organic
waste products
• Assists liver
• In detoxifying poisons
© 2015 Pearson Education, Inc.
Figure 26-2a The Position of the Kidneys.
Adrenal gland
Diaphragm
11th and
12th ribs
Left kidney
L1 vertebra
Right kidney
Ureter
Renal artery
and vein
Inferior
vena cava
Iliac crest
Aorta
Urinary
bladder
Urethra
a A posterior view of the trunk
© 2015 Pearson Education, Inc.
Figure 26-2b The Position of the Kidneys.
External
oblique
Parietal
peritoneum
Stomach
Renal
vein
Renal
artery
Aorta
Pancreas
Ureter
Spleen
Left
kidney
Vertebra
Connective
tissue layers
Fibrous capsule
Perinephric fat
Renal fascia
Quadratus
lumborum
Psoas
major
Inferior
vena cava
b A superior view of a transverse section
at the level indicated in part (a)
© 2015 Pearson Education, Inc.
Figure 26-3 The Gross Anatomy of the Urinary System.
Esophagus (cut)
Diaphragm
Left adrenal gland
Inferior vena cava
Left kidney
Celiac trunk
Left renal artery
Right adrenal gland
Left renal vein
Right kidney
Superior mesenteric
artery
Hilum
Quadratus lumborum
muscle
Left ureter
Abdominal aorta
Iliacus muscle
Left common
iliac artery
Psoas major muscle
Gonadal artery
and vein
Peritoneum (cut)
Rectum (cut)
Urinary bladder
Anterior view
© 2015 Pearson Education, Inc.
26-2 The Kidneys
• Sectional Anatomy of the Kidneys
• Renal sinus
• Internal cavity within kidney
• Lined by fibrous renal capsule
• Bound to outer surfaces of structures in renal sinus
• Stabilizes positions of ureter, renal blood vessels,
and nerves
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26-2 The Kidneys
• Renal Cortex
• Superficial portion of kidney in contact with renal
capsule
• Reddish brown and granular
• Renal Pyramids
• 6 to 18 distinct conical or triangular structures in
renal medulla
• Base abuts cortex
• Tip (renal papilla) projects into renal sinus
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26-2 The Kidneys
• Renal Columns
• Bands of cortical tissue separate adjacent renal
pyramids
• Extend into medulla
• Have distinct granular texture
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26-2 The Kidneys
• Kidney Lobe
• Consists of:
• Renal pyramid
• Overlying area of renal cortex
• Adjacent tissues of renal columns
• Produces urine
• Kidney receives blood through renal artery
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26-2 The Kidneys
• Renal Papilla
• Ducts discharge urine into minor calyx, a cupshaped drain
• Major Calyx
• Formed by four or five minor calyces
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26-2 The Kidneys
• Renal Pelvis
•
•
•
•
Large, funnel-shaped chamber
Consists of two or three major calyces
Fills most of renal sinus
Connected to ureter, which drains kidney
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Figure 26-4a The Structure of the Kidney.
Renal cortex
Renal medulla
Inner layer of
fibrous capsule
Renal pyramid
Renal sinus
Connection to
minor calyx
Adipose tissue
in renal sinus
Minor calyx
Renal pelvis
Major calyx
Hilum
Kidney lobe
Renal papilla
Renal columns
Ureter
Fibrous capsule
a A diagrammatic view of a frontal
section through the left kidney
© 2015 Pearson Education, Inc.
Figure 26-4b The Structure of the Kidney.
Renal cortex
Renal medulla
Renal
pyramids
Renal sinus
Renal pelvis
Major calyx
Hilum
Minor calyx
Ureter
Renal papilla
Renal columns
Kidney lobe
Fibrous
capsule
b A frontal section of the
left kidney (cadaver)
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26-2 The Kidneys
• Nephrons
• Microscopic, tubular structures in cortex of each
renal lobe
• Where urine production begins
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26-2 The Kidneys
• Sympathetic Innervation
• Adjusts rate of urine formation
• By changing blood flow and blood pressure at
nephron
• Stimulates release of renin
• Which restricts losses of water and salt in urine
• By stimulating reabsorption at nephron
© 2015 Pearson Education, Inc.
Figure 26-5a The Blood Supply to the Kidneys.
Cortical
radiate
veins
Cortical
radiate
arteries
Interlobar
arteries
Cortex
Segmental
artery
Adrenal
artery
Renal
artery
Renal
vein
Arcuate
veins
Interlobar
veins
Medulla
Arcuate
arteries
a A sectional view, showing major
arteries and veins
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Figure 26-5b The Blood Supply to the Kidneys.
Glomerulus
Cortical radiate vein
Afferent
arterioles
Cortical radiate artery
Arcuate artery
Cortical
nephron
Arcuate vein
Juxtamedullary
nephron
Renal
pyramid
Interlobar vein
Interlobar artery
Minor calyx
b Circulation in a single kidney lobe
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26-2 The Kidneys
• The Nephron
• Consists of renal tubule and renal corpuscle
• Renal tubule
• Long tubular passageway
• Begins at renal corpuscle
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26-2 The Kidneys
• The Nephron
• Renal corpuscle
• Spherical structure consisting of:
• Glomerular capsule (Bowman’s capsule)
• Cup-shaped chamber
• Capillary network (glomerulus)
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26-2 The Kidneys
• Glomerulus
• Consists of 50 intertwining capillaries
• Blood delivered via afferent arteriole
• Blood leaves in efferent arteriole
• Flows into peritubular capillaries
• Which drain into small venules
• And return blood to venous system
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26-2 The Kidneys
• Filtration
• Occurs in renal corpuscle
• Blood pressure
• Forces water and dissolved solutes out of
glomerular capillaries into capsular space
• Produces protein-free solution (filtrate) similar to
blood plasma
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26-2 The Kidneys
• Three Functions of the Renal Tubule
1. Reabsorb useful organic nutrients that enter
filtrate
2. Reabsorb more than 90 percent of water in
filtrate
3. Secrete waste products that failed to enter renal
corpuscle through filtration at glomerulus
© 2015 Pearson Education, Inc.
26-2 The Kidneys
• Segments of the Renal Tubule
• Located in cortex
• Proximal convoluted tubule (PCT)
• Distal convoluted tubule (DCT)
• Separated by nephron loop (loop of Henle)
• U-shaped tube
• Extends partially into medulla
© 2015 Pearson Education, Inc.
Figure 26-6 The Functional Anatomy of a Representative Nephron and the Collecting System (Part 1 of 2).
NEPHRON
Proximal convoluted tubule
Distal convoluted tubule
• Reabsorption of water, ions,
and all organic nutrients
• Secretion of ions, acids, drugs, toxins
• Variable reabsorption of water, sodium ions,
and calcium ions (under hormonal control)
Cuboidal cells
with abundant
microvilli
Cuboidal cells
with few microvilli
Mitochondria
Renal
tubule
Renal corpuscle
• Production of filtrate
Squamous cells
Efferent arteriole
Afferent arteriole
Glomerulus
Glomerular capsule
Descending
limb of
loop begins
Capsular space
Ascending
limb of
loop ends
Nephron loop
Squamous cells
Low cuboidal cells
Descending limb
Further reabsorption
of water
Ascending limb
Reabsorption of
sodium and
chloride ions
Thick
ascending
limb
Thin
descending
limb
KEY
Filtrate
Water reabsorption
Variable water
reabsorption
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Solute reabsorption
or secretion
Variable solute
reabsorption or
secretion
26-2 The Kidneys
• Organization of the Nephron
• Traveling along tubule, filtrate (tubular fluid)
gradually changes composition
• Changes vary with activities in each segment of
nephron
© 2015 Pearson Education, Inc.
26-2 The Kidneys
• Each Nephron
• Empties into the collecting system
• A series of tubes that carries tubular fluid away
from nephron
• Collecting ducts
• Receive fluid from many nephrons
• Each collecting duct:
• Begins in cortex
• Descends into medulla
• Carries fluid to papillary duct that drains into a minor
calyx
© 2015 Pearson Education, Inc.
Figure 26-6 The Functional Anatomy of a Representative Nephron and the Collecting System (Part 2 of 2).
COLLECTING SYSTEM
Collecting duct
• Variable reabsorption of water
and reabsorption or secretion of
sodium, potassium, hydrogen,
and bicarbonate ions
Intercalated
cell
Principal cell
KEY
Filtrate
Papillary duct
Water reabsorption
• Delivery of urine to minor calyx
Variable water
reabsorption
Solute reabsorption
or secretion
Variable solute
reabsorption or
secretion
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Minor
calyx
Columnar cells
Figure 26-7b The Locations and Structures of Cortical and Juxtamedullary Nephrons.
Peritubular capillaries
Efferent
arteriole
Distal
convoluted
tubule
Afferent
arteriole
Renal
corpuscle
Collecting
duct
Peritubular
capillaries
Nephron
loop
b The circulation to a
cortical nephron
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Figure 26-7c The Locations and Structures of Cortical and Juxtamedullary Nephrons.
Peritubular
capillaries
Proximal
convoluted
tubule (PCT)
Distal
convoluted
tubule (DCT)
Renal
corpuscle
Collecting
duct
Vasa recta
Nephron
loop
c The circulation to a
juxtamedullary nephron
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26-2 The Kidneys
• The Renal Corpuscle
• Each renal corpuscle is 150–250 µm in diameter
• Glomerular capsule
• Is connected to initial segment of renal tubule
• Forms outer wall of renal corpuscle
• Encapsulates glomerular capillaries
• Glomerulus
• Knot of capillaries
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26-2 The Kidneys
• The Glomerular Capsule
• Outer wall is lined by simple squamous capsular
epithelium
• Continuous with visceral epithelium that covers
glomerular capillaries
• Separated by capsular space
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26-2 The Kidneys
• The Visceral Epithelium
• Consists of large cells (podocytes)
• With complex processes or “feet” (pedicels) that
wrap around specialized dense layer of glomerular
capillaries
• Filtration Slits
• Are narrow gaps between adjacent pedicels
• Materials passing out of blood at glomerulus:
• Must be small enough to pass between filtration
slits
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Figure 26-8a The Renal Corpuscle.
Glomerular capsule
Capsular
space
Efferent arteriole
Glomerular
capillary
Capsular
epithelium
Visceral
epithelium
(podocyte)
Proximal
convoluted
tubule
Distal convoluted
tubule
Juxtaglomerular
complex
Macula densa
Juxtaglomerular
cells
Afferent arteriole
a Important structural features of a renal corpuscle.
© 2015 Pearson Education, Inc.
Figure 26-8b The Renal Corpuscle.
Filtration
membrane
Podocyte
nucleus
Fenestrated
endothelium
Dense layer
Filtration
slits
Capillary
endothelial
cell
Mesangial
cell
Pores
RBC
Pedicels
Podocyte
Capsular space
Capsular
epithelium
b This cross section through a portion of
the glomerulus shows the components of
the filtration membrane of the nephron.
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26-2 The Kidneys
• The Glomerular Capillaries
• Are fenestrated capillaries
• Endothelium contains large-diameter pores
• Blood Flow Control
• Special supporting cells (mesangial cells)
• Between adjacent capillaries
• Control diameter and rate of capillary blood flow
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26-2 The Kidneys
• Filtration
• Blood pressure
• Forces water and small solutes across membrane
into capsular space
• Larger solutes, such as plasma proteins, are
excluded
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26-2 The Kidneys
• Filtration at Renal Corpuscle
• Is passive
• Solutes enter capsular space
• Metabolic wastes and excess ions
• Glucose, free fatty acids, amino acids, and vitamins
• Reabsorption
• Useful materials are recaptured before filtrate
leaves kidneys
• Reabsorption occurs in proximal convoluted tubule
© 2015 Pearson Education, Inc.
26-2 The Kidneys
• The Proximal Convoluted Tubule (PCT)
• Is the first segment of renal tubule
• Entrance to PCT lies opposite point of connection
of afferent and efferent arterioles with glomerulus
• Epithelial Lining of PCT
•
•
•
•
Is simple cuboidal
Has microvilli on apical surfaces
Functions in reabsorption
Secretes substances into lumen
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26-2 The Kidneys
• Tubular Cells
• Absorb organic nutrients, ions, water, and plasma
proteins from tubular fluid
• Release them into peritubular fluid (interstitial
fluid around renal tubule)
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26-2 The Kidneys
• The Nephron Loop (Loop of Henle)
• Renal tubule turns toward renal medulla
• Descending limb
• Fluid flows toward renal pelvis
• Thick segment: Pumps sodium and chloride ions
out of tubular fluid
• Ascending limb
• Fluid flows toward renal cortex
• Reabsorb sodium & chloride ions
• Thin segments: Are freely permeable to water (not
solutes)
© 2015 Pearson Education, Inc.
Figure 26-6 The Functional Anatomy of a Representative Nephron and the Collecting System (Part 1 of 2).
NEPHRON
Proximal convoluted tubule
Distal convoluted tubule
• Reabsorption of water, ions,
and all organic nutrients
• Secretion of ions, acids, drugs, toxins
• Variable reabsorption of water, sodium ions,
and calcium ions (under hormonal control)
Cuboidal cells
with abundant
microvilli
Cuboidal cells
with few microvilli
Mitochondria
Renal
tubule
Renal corpuscle
• Production of filtrate
Squamous cells
Efferent arteriole
Afferent arteriole
Glomerulus
Glomerular capsule
Descending
limb of
loop begins
Capsular space
Ascending
limb of
loop ends
Nephron loop
Squamous cells
Low cuboidal cells
Descending limb
Further reabsorption
of water
Ascending limb
Reabsorption of
sodium and
chloride ions
Thick
ascending
limb
Thin
descending
limb
KEY
Filtrate
Water reabsorption
Variable water
reabsorption
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Solute reabsorption
or secretion
Variable solute
reabsorption or
secretion
26-2 The Kidneys
• The Distal Convoluted Tubule (DCT)
• The third segment of the renal tubule
• Initial portion passes between afferent and efferent
arterioles
• Has a smaller diameter than PCT
• Epithelial cells lack microvilli
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26-2 The Kidneys
• Three Processes at the DCT
1. Active secretion of ions, acids, drugs, and toxins
2. Selective reabsorption of sodium and calcium
ions from tubular fluid
3. Selective reabsorption of water
• Concentrates tubular fluid
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26-2 The Kidneys
• The Juxtaglomerular Complex (JGC)
• An endocrine structure that secretes:
• Hormone erythropoietin
• Enzyme renin
• Formed by:
• Macula densa
• Juxtaglomerular cells
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Figure 26-8a The Renal Corpuscle.
Glomerular capsule
Capsular
space
Efferent arteriole
Glomerular
capillary
Capsular
epithelium
Visceral
epithelium
(podocyte)
Proximal
convoluted
tubule
Distal convoluted
tubule
Juxtaglomerular
complex
Macula densa
Juxtaglomerular
cells
Afferent arteriole
a Important structural features of a renal corpuscle.
© 2015 Pearson Education, Inc.
26-2 The Kidneys
• The Collecting System
• The distal convoluted tubule opens into the
collecting system
• Individual nephrons drain into a nearby collecting
duct
• Several collecting ducts:
• Converge into a larger papillary duct
• Which empties into a minor calyx
• Transports tubular fluid from nephron to renal pelvis
• Adjusts fluid composition
• Determines final osmotic concentration and volume
of urine
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26-3 Renal Physiology
• The Goal of Urine Production
• Is to maintain homeostasis
• By regulating volume and composition of blood
• Including excretion of metabolic waste products
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26-3 Renal Physiology
• Three Organic Waste Products
1. Urea
2. Creatinine
3. Uric acid
• Organic Waste Products
• Are dissolved in bloodstream
• Are eliminated only while dissolved in urine
• Removal is accompanied by water loss
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26-3 Renal Physiology
• The Kidneys
• Usually produce concentrated urine
• 1200–1400 mOsm/L (four times plasma
concentration)
• Kidney Functions
• To concentrate filtrate by glomerular filtration
• Failure leads to fatal dehydration
• Absorbs and retains valuable materials for use by
other tissues
• Sugars and amino acids
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26-3 Renal Physiology
• Basic Processes of Urine Formation
1. Filtration
2. Reabsorption
3. Secretion
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26-3 Renal Physiology
• An Overview of Renal Function
• Water and solute reabsorption
• Primarily along proximal convoluted tubules
• Active secretion
• Primarily at proximal and distal convoluted tubules
• Long loops of juxtamedullary nephrons and
collecting system
• Regulate final volume and solute concentration of
urine
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Figure 26-9 An Overview of Urine Formation.
Proximal convoluted
tubule
Distal convoluted
tubule
Glomerulus
Glomerular
capsule
Collecting
duct
KEY
Filtration occurs exclusively in the renal corpuscle,
across the filtration membrane.
Nephron
loop
Water reabsorption occurs primarily along the PCT and
the descending limb of the nephron loop, but also to a
variable degree in the DCT and collecting system.
Variable water reabsorption occurs in the DCT and
collecting system.
Solute reabsorption occurs along the PCT, the
ascending limb of the nephron loop, the DCT, and
the collecting system.
Variable solute reabsorption or secretion occurs at
the PCT, the DCT, and the collecting system.
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Urine storage
and elimination
Table 26-2 Normal Laboratory Values for Solutes in Plasma and Urine.
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26-3 Renal Physiology
• Renal Threshold for Glucose
• Is approximately 180 mg/dL
• If plasma glucose is greater than 180 mg/dL:
• Tm of tubular cells is exceeded
• Glucose appears in urine
• Glycosuria
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26-3 Renal Physiology
• Renal Threshold for Amino Acids
• Is lower than glucose (65 mg/dL)
• Amino acids commonly appear in urine
• After a protein-rich meal
• Aminoaciduria
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Table 26-3 Tubular Reabsorption and Secretion.
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Figure 26-11 The Response to a Reduction in the GFR (Part 2 of 2).
Autoregulation
Immediate local
response in the
kidney
Increased
glomerular
blood pressure
Dilation of
afferent arterioles
Contraction of
mesangial cells
Constriction of
efferent arterioles
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if sufficient
HOMEOSTASIS
RESTORED
Normal
GFR
HOMEOSTASIS
DISTURBED
Decreased GFR
resulting in
decreased filtrate
and urine
production
HOMEOSTASIS
Start
Normal
glomerular
filtration rate
26-4 Glomerular Filtration
• Hormonal Regulation of the GFR (glomeral
filtration)
• By hormones of the:
• Renin–angiotensin-aldosterone system
• Natriuretic peptides (ANP and BNP)
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26-4 Glomerular Filtration
• The Renin–Angiotensin-Aldosterone System
• Three stimuli cause the juxtaglomerular complex
(JGC) to release renin
1. Decline in blood pressure at glomerulus due to
decrease in blood volume, fall in systemic
pressures, or blockage in renal artery or tributaries
2. Stimulation of juxtaglomerular cells by sympathetic
innervation
3. Decline in osmotic concentration of tubular fluid at
macula densa
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26-4 Glomerular Filtration
• The Renin–Angiotensin-Aldosterone System:
Angiotensin II Activation
• Constricts efferent arterioles of nephron
• Elevating glomerular pressures and filtration rates
• Stimulates reabsorption of sodium ions and water
at PCT
• Stimulates secretion of aldosterone by adrenal
cortex
• Stimulates thirst
• Triggers release of antidiuretic hormone (ADH)
• Stimulates reabsorption of water in distal portion of
DCT and collecting system
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26-4 Glomerular Filtration
• The Renin–Angiotensin-Aldosterone System
• Aldosterone
• Accelerates sodium reabsorption in DCT and
cortical portion of collecting system
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Figure 26-11 The Response to a Reduction in the GFR (Part 1 of 2).
Renin–Angiotensin-Aldosterone System
Integrated endocrine and
neural mechanisms activated
Endocrine
response
Juxtaglomerular
complex increases
production of renin
Renin in the bloodstream
triggers formation of
angiotensin I, which is then
activated to angiotensin II
by angiotensin converting
enzyme (ACE) in the
capillaries of the lungs
Angiotensin II constricts
peripheral arterioles and
further constricts the
efferent arterioles
HOMEOSTASIS
RESTORED
Increased
glomerular
pressure
Increased
systemic
blood
pressure
Increased
blood
volume
Angiotensin II triggers
increased aldosterone
secretion by the
adrenal glands
Angiotensin II
triggers
neural
responses
Aldosterone
increases
Na+ retention
Increased fluid
consumption
Increased
stimulation of
thirst centers
Increased fluid
retention
Increased ADH
production
Constriction of
venous reservoirs
Increased
cardiac output
Together, angiotensin II
and sympathetic activation
stimulate peripheral
vasoconstriction
HOMEOSTASIS
Normal
glomerular
filtration rate
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Increased
sympathetic
motor tone
26-4 Glomerular Filtration
• Hormonal Regulation of the GFR
• Increased Blood Volume
• Automatically increases GFR
• To promote fluid loss
• Hormonal factors further increase GFR
• Accelerating fluid loss in urine
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26-5 Reabsorption and Secretion
• Reabsorption
• Recovers useful materials from filtrate
• Secretion
• Ejects waste products, toxins, and other
undesirable solutes
• Reabsorption and Secretion
• Occur in every segment of nephron
• Except renal corpuscle
• Relative importance changes from segment to
segment
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26-5 Reabsorption and Secretion
• Aldosterone
• Is a hormone produced by the adrenal cortex
• Controls ion pump and channels
• Stimulates synthesis and incorporation of Na+
pumps and channels
• In plasma membranes along DCT and collecting
duct
• Reduces Na+ lost in urine
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26-5 Reabsorption and Secretion
• Hypokalemia
• Produced by prolonged aldosterone stimulation
• Dangerously reduces plasma concentration
• Natriuretic Peptides (ANP and BNP)
• Oppose secretion of aldosterone
• And its actions on DCT and collecting system
• Parathyroid Hormone and Calcitriol
• Circulating levels regulate calcium ion
reabsorption at the DCT
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26-5 Reabsorption and Secretion
• Hydrogen Ion Secretion
• Acidifies tubular fluid
• Elevates blood pH
• Accelerates when blood pH falls
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26-5 Reabsorption and Secretion
• Acidosis
• Lactic acidosis
• Develops after exhaustive muscle activity
• Ketoacidosis
• Develops in starvation or diabetes mellitus
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26-5 Reabsorption and Secretion
• Control of Blood pH
• By H+ removal and bicarbonate production at
kidneys
• Is important to homeostasis
• Alkalosis
• Abnormally high blood pH
• Can be caused by prolonged aldosterone
stimulation (Na+ retention coupled with H+
secretion)
• Which stimulates secretion
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26-5 Reabsorption and Secretion
• Regulating Water and Solute Loss in the
Collecting System
• By aldosterone
• Controls sodium ion pumps
• Actions are opposed by natriuretic peptides
• By ADH
• Controls permeability to water
• Is suppressed by natriuretic peptides
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26-5 Reabsorption and Secretion
• ADH
• Hormone that causes special water channels
(aquaporins) to appear in apical cell membranes
• Increases rate of osmotic water movement
• Higher levels of ADH increase:
• Number of water channels
• Water permeability of DCT and collecting system
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26-5 Reabsorption and Secretion
• Without ADH:
• Water is not reabsorbed
• All fluid reaching DCT is lost in urine
• Producing large amounts of dilute urine
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26-5 Reabsorption and Secretion
• The Hypothalamus
• Continuously secretes low levels of ADH
• DCT and collecting system are always permeable
to water
• At normal ADH levels
• Collecting system reabsorbs 16.8 liters/day (9.3
percent of filtrate)
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26-5 Reabsorption and Secretion
• Urine Production
• A healthy adult produces:
• 1200 mL per day (0.6 percent of filtrate)
• With osmotic concentration of 855–1335 mOsm/L
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26-5 Reabsorption and Secretion
• Diuresis
• Is the elimination of urine
• Typically indicates production of large volumes of
urine
• Diuretics
• Are drugs that promote water loss in urine
• Diuretic therapy reduces:
• Blood volume
• Blood pressure
• Extracellular fluid volume
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26-5 Reabsorption and Secretion
• The Composition of Normal Urine
• A urine sample depends on osmotic movement of
water across walls of tubules and collecting ducts
• Is a clear, sterile solution
• Yellow color (pigment urobilin)
• Generated in kidneys from urobilinogens
• Urinalysis, the analysis of a urine sample, is an
important diagnostic tool
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Table 26-5 General Characteristics of Normal Urine.
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Table 26-6 Typical Values Obtained from Standard Urinalysis (Part 1 of 4).
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Table 26-6 Typical Values Obtained from Standard Urinalysis (Part 2 of 4).
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Table 26-6 Typical Values Obtained from Standard Urinalysis (Part 3 of 4).
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Table 26-6 Typical Values Obtained from Standard Urinalysis (Part 4 of 4).
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26-6 Urine Transport, Storage, and
Elimination
• Urine Transport, Storage, and Elimination
• Take place in the urinary tract
• Ureters
• Urinary bladder
• Urethra
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Figure 26-17 A Pyelogram.
11th and
12th ribs
Ureter
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Urinary
bladder
Minor
calyx
Renal
pelvis
Major
calyx
Kidney
26-6 Urine Transport, Storage, and
Elimination
• The Ureters
•
•
•
•
Are a pair of muscular tubes
Extend from kidneys to urinary bladder
Begin at renal pelvis
Ureteral openings are slit-like rather than
rounded
• Shape helps prevent backflow of urine when
urinary bladder contracts
• Peristaltic Contractions of ureters move urine
toward bladder
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Figure 26-19a The Histology of the Ureter, Urinary Bladder, and Urethra.
Transitional
epithelium
Mucosa
Lamina
propria
Smooth
muscle
Outer connective
tissue layer
Ureter
LM ×65
a A transverse section through the ureter.
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26-6 Urine Transport, Storage, and
Elimination
• Peristaltic Contractions
•
•
•
•
Begin at renal pelvis
Sweep along ureter
Force urine toward urinary bladder
Every 30 seconds
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26-6 Urine Transport, Storage, and
Elimination
• The Urinary Bladder
• Is a hollow, muscular organ
• Functions as temporary reservoir for urine storage
• Full bladder can contain 1 liter of urine
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Figure 26-18a Organs for Conducting and Storing Urine.
Left ureter
Peritoneum
Urinary
bladder
Pubic
symphysis
Prostate
gland
External
urethral
sphincter
Spongy
urethra
External
urethral
orifice
Urethra
[see part c]
a Male
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Urogenital
diaphragm
Rectum
Figure 26-18b Organs for Conducting and Storing Urine.
Rectum
Right ureter
Uterus
Peritoneum
Urinary
bladder
Internal
urethral
sphincter
Pubic
symphysis
Urethra
External
urethral
sphincter (in
urogenital
diaphragm)
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Vestibule
Vagina
b Female
Figure 26-18c Organs for Conducting and Storing Urine.
Median umbilical
ligament
Ureter
Lateral
umbilical
ligament
Detrusor
muscle
Rugae
Ureteral
openings
Center of trigone
Neck of
urinary bladder
Internal urethral
sphincter
Prostate gland
External urethral
sphincter (in urogenital
diaphragm)
Prostatic urethra
Membranous urethra
c Urinary bladder in male
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26-6 Urine Transport, Storage, and
Elimination
• The Urethra
• Extends from neck of urinary bladder
• To the exterior of the body
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26-6 Urine Transport, Storage, and
Elimination
• The Female Urethra
• Is very short (3–5 cm; 1–2 in.)
• Extends from bladder to vestibule
• External urethral orifice is near anterior wall of
vagina
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26-6 Urine Transport, Storage, and
Elimination
• The External Urethral Sphincter
• In both sexes
• Is a circular band of skeletal muscle
• Where urethra passes through urogenital
diaphragm
• Acts as a valve
• Is under voluntary control
• Via perineal branch of pudendal nerve
• Has resting muscle tone
• Voluntary relaxation permits micturition
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26-6 Urine Transport, Storage, and
Elimination
• The Micturition Reflex and Urination
• As the bladder fills with urine:
• Stretch receptors in urinary bladder stimulate
sensory fibers in pelvic nerve
• Stimulus travels from afferent fibers in pelvic
nerves to sacral spinal cord
• Efferent fibers in pelvic nerves:
• Stimulate ganglionic neurons in wall of bladder
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26-6 Urine Transport, Storage, and
Elimination
• The Micturition Reflex and Urination
• Postganglionic neuron in intramural ganglion
stimulates detrusor muscle contraction
• Interneuron relays sensation to thalamus
• Projection fibers from thalamus deliver sensation
to cerebral cortex
• Voluntary relaxation of external urethral sphincter
causes relaxation of internal urethral sphincter
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Figure 26-20 The Micturition Reflex (Part 1 of 2).
L2 Senory
Parasympathetic
L3 preganglionic
fibers in
pelvic
nerves.
motor fibers in
pelvic nerves.
L1 Distortion
Urinary
bladder
of stretch
receptors.
ganglia stimulate
detrusor muscle
contraction.
Start
C4
Voluntary relaxation of the
external urethral sphincter
causes relaxation of the
internal urethral sphincter.
Urination occurs
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Postganglionic
L4 neurons in intramural
Figure 26-20 The Micturition Reflex (Part 2 of 2).
C2
Projection fibers
from thalamus
deliver sensation
to the cerebral
cortex.
C1
An interneuron
relays sensation
to the thalamus.
Brain
If convenient, the
C3 individual voluntarily
relaxes the external
urethral sphincter.
The afferent fibers
stimulate neurons
involved with:
L a local pathway,
and
C a central pathway
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26-6 Urine Transport, Storage, and
Elimination
• Infants
• Lack voluntary control over urination
• Corticospinal connections are not established
• Incontinence
• Is the inability to control urination voluntarily
• May be caused by trauma to internal or external
urethral sphincter
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26-7 Effects of Aging on the Urinary System
• Age-Related Changes
•
•
•
•
Decline in number of functional nephrons
Reduction in GFR
Reduced sensitivity to ADH
Problems with micturition reflex
• Sphincter muscles lose tone leading to
incontinence
• Control of micturition can be lost due to a stroke,
Alzheimer’s disease, and other CNS problems
• In males, urinary retention may develop if enlarged
prostate gland compresses the urethra and
restricts urine flow
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